Electrooptical system



May 5, 1931. F. GRAY 1,803,700

ELECTROOPTICAL SYSTEM Filed July 2'5, 1929 DEM BPF

/Ni/E/v TUR F GRAY Patented May 5, 1931 y UNITED lSTATES PATENT OFFICE FRANK GRAY, or NEwYoRx, N. Y., AssIeNoR 'ro RELL TELErRoNE LABORATORIES, INcoRroRA'i-ED, or NEW YORK, N. Y., A CORPORATION or NEW YORK ELCTROOPTlCAL SYSTEM Application ma July 25, 1929. serial No. 380,786.

This invention relates to electro-optical systems and more particularly to a method of and apparatus for producing television images. Y

`A11 object of the invention is to provide a simple method and means for producing a photo-electric current having components which correspond respectively,'to simultaneously scanned elemental areas of a field of view and which can be separated and separately utilized as desired, for example, for multi-transmission line television.

Another object of the inventionV is to provide novel means for producing a beam of light modulated at a definite frequency.

Ink apreferred embodiment of the invention,`a scanning disc having apertures arranged in the form of a spiral of two convolutions is employed to project two beams of light simultaneously upon the field of view so that the field is scanned by two spots ofy `light moving over different courses. Each of these beams is interrupted or modulated at a distinctive frequency. Light reflected from the field of view may be received upon a single photoelectric cell and the resulting variations impressed upon frequency selective means for separat-ing Vthe components of different constant frequency. The interrupting or modulating of the light beams is preferably accomplished by providing a grating of closely spaced parallel rulings over each of the apertures of the scanning disc, the

spacing of the lines being different'for one Y convolution of the spiral than for the other.

Separate stationary gratings are provided one for each convolution of the spiral having, respectively, Vthe same'spacing of rulingsas the apertures of the corresponding convolution of the spiral. The gratingsare preferably soY designed as. to have rulings varying in opaqueness from the center to the edge to produce variations in the light beam in a sinusoidal manner. A large number of beams may, of course, be employed and any suitable means used to direct and rmodulate the beams. The image current produced as the result of scanning and comprising a plurality of modulated `fre uency components, are preferably separated ymeans of filters,

,passing through the apertures of the inner demodulated and transmitted over separate transmission lines respectively.

A television system embodying features of this invention is shown diagrammatically in Fig. 1 of the accompanying drawing;

Fig.,2 is an enlarged fragmentary view showing in detail the construction of the scanning disc employed at the transmitting station of the system shown inV Fig. l; and

Fig. 3 is an enlarged sectional view of a portion of the'disc employed at the receiving station.

Referring to the drawing, a eld of view comprising the subject 10 is scanned by light from a source 11 as it passes through the apertures 14.- in the scanningY disc 12 `which is driven by the motor 13 at the rate of 16 or more revolutions per second. The aper tures 14 in the scanning disc are arranged in the form of a spiral of two convolutions although an arrangement employing a spiral having a greater number of convolutions may be employed. As the disc rotates, two separate portions of the subject 10 are scanned simultaneously by lmeans of. two moving 75 light beams. The lightrpassing through the apertures of the outer convolution of the spiral is deflected by the lens 15 so as to scan the lower half of the subject 10 and the .light 8o convolution ofthe spiral is deflected Vby the same lens so as to scan the upper half of the subject. A.

Each aperture of the Vscanning disc isV covered witha grating lcomprising alternate opaque and translucent lines.' The width-of the lines ofthe grating. 2O is the same for all of the apertures of the. outer convolution of i the spiral. The width of the lines of the grat-'i ing 21 Acovering the apertures of the inner 90 convolution of the spiral Vis greater ory less than the width of the lines of the grating 20. The screen `16 having Van opening therein which defines the field of view is preferably positioned close to the disc 12 either between the disc and the lens 15 or on the opposite side of the disc. The opening in the screen Y 16 is covered by two gratings, the grating 22 covering the upper half of the opening being Asimilar to thelone covering the apertures of 1GO the outer convolution of the spiral in the scan ning disc and the grating 23 covering the loiver half of the opening being similar to the grat-ing 21 covering the apertures of the inner convolution. The gratings may be made, for example, by the use of an engraving ma.- chine or by ruling relatively Wide lines and reducing them photographically. Another method of making the gratings is to move al sensitized film slowly in front of a line source of light Which is energized by an alternating current of suitable frequency. In this case the opacity of the lines varies gradually so as to produce a sine Wave fiuctuation of light intensity. However, the sine Wave is sufficiently closely approximated for most purposes by the alternate opaque and translucent lines cach of which has uniform light transmitting properties throughout their Width.

lt is thus apparent that each of the light beams Whichscans the subject 10 is infierrupted or changed in i' nsity periodically at a high frequency, the frequency of inter ruption being greater for one beam than 'for the other. Light reflected from the subject 10 impinges on thelight sensitive or photoclectric cell 17 and causes the current in the circuit of the cell to vary in accordance with the variations in light intensity. This current has two frequency components, one corresponding to the rate at Which the light beam passing through the gratings 20 and is interrupted and the other frequency component corresponding to the rate at which the other light beam is interrupted by the gratnigs 21 and 23. These light beams illuminate, successively, elemental areas of different portions, rfe-spectively, of the subject l0. Each of the frequency components of the photo electric current is therefore modulated in accordance with the tone mir-.es of the suecessively illuminated elemental areas of one of the portionsof the field of view. i After being suitably amplified by the amplifier 24, the two modulated frequency components of the i-mage current are separated by the bandpass filters 25 and 26. rlhe two currents which correspond to the two components of the `photoelectric current are then demodu'- lated by the demodulators 27 and 28, respectively, and amplified by the amplifiers 29 and 30, respectively. vOne de'modulated current having amplitude Avariations corresponding to the tone values of successively scanned elemental areas of one portion of the field of vienv is transmitted through transformer 31 and over the line 33 to the receiving station, where it is transmitted through transformer 35 and amplifier 3T and impressed on the neon glow discharge lamp 39. Theother demodulated current having amplitude variations corresponding to the tone values of the successively scanned elemental areas of another portion of the field of view is similarly trans` mitted over a circuit comprising the transformer 32, transmission line 34, transformer 3G and amplifier 38 to the neon glow discharge lamp 40.

The disc 41 Which has the same number of apertures'43 as the disc 12, and similarly arraged in a spiral of two convolutions, is

driven by the motor 42 in synchronism with the disc 12. A system such as that disclosed in Patent No. 1,763,909, granted to H. M. Stoller and E. R. Morton, June 17, 1930, may be employed for controlling the speed of the motors 13 and 42 so as to maintain the discs 12 and 41 in synchronism and in phase. A prism is positioned over each aperture 43 in the disc 4iso that light from `the lamp `39 is transmitted.through the apertures of the outer lconvolution of the spiral and so that light from thelamp istransmitted through the apertures of the inner convolution 4of the iral the position of the apertures changes ect to the position Vof the lamps due to the rotation of the disc 4l. A similar arrangement' employing prisms' over the apertures of the scanning dise is disclosed in a eopending aplulication of H. E. Ives,`Serial No. 291,744, fi ed July 11, 1928. Mince the field oi' view is completely scanned 16 or more times per second, Which is within the period of 'the persi. `ence of vision, the observer 45, as lic looks into the opening in the frame 45, see i an image of the field of view comprising thel subject lO'Which may be moving or changnig.

` That is claimed is:

1. A device for scanning a field of view comprising a movable element of opaque material, and ar light aperture having alternate sections of relatively opaque and transparent material arranged in said movable element.

2. A device for scanning la field ofV view comprising a movable element of opaque materia-l, and a plurality of light apertures -arranged therein, each aperture comprising .a plurality of sections the opacity of which varies gradually from one portion of the section to another.

3. A device for vscanning a field of view comprising a movable.element of opaque material `having a plurality of apertures therein, and a grating of alternate transparent and opaque elements secured to said movable element and positioned over said apertures.

4. A seanningdisc comprising a plurality of apertures, and means secured to said scanning disc and associated with each aperture thereof for breaking up the beam of light passing therethrough into a plurality of separate, substantially parallel rays.

5. Means for modulating lightcomprising a source of light, a cyc'lically moving member having a plurality ofv light apertures, a grating for each light aperture and moving therewith, and a stationary grating aligned with said moving element and said source so ilo that the stationary grating and said source are successively optically aligned with said light apertures.

6. Means for scanning a eld of view to produce an image current which comprises a source of light, a movable element having light apertures therein for directing light from said source upon elemental areas of said field of view in succession, means for periodically interrupting the illumination of an elemental area of the field of view, said means comprising a stationary grating in the light path and a grating positioned over the apertures of the scanning disc, and light sensitive means for receiving light from the illuminated elemental area of the field of view to produce an image current.

7 In an electro-optical image producing system a source of light, a scanning disc having a plurality of light aperturesV therein arranged in a spiral of a plurality of convolutions for scanning a plurality of portions of said field of view simultaneously, means comprising a grating positioned over the aper' tures of the scanning disc for interrupting the light transmitted by the apertures of different convolutions at different high frevquencies respectively, light sensitive means for receiving light from the elemental areas of the field of view and for setting up an image current having components correspending to the frequencies at which the different light beams respectively'are interrupted, and means for producing sepa-rate currents corresponding to the different frequency components respectively of said im-age current for controlling the production of an image of said field of view.

In witness whereof, I hereunto subscribe my name this 24th day of July, 1929.

FRANK GRAY. 

